1. Field of the Invention
The present invention relates to an edge-holding aligner capable of holding an edge of a substrate and turning the substrate to adjust the position of the substrate.
2. Description of the Related Art
A disk-shaped substrate, such as a semiconductor wafer, has an orientation indicator, such as a notch or an orientation flat, for indicating a reference position in a circumferential direction. The notch is a V-shaped indentation cut in the edge of the substrate. The orientation flat is a chord formed by cutting a segment from a peripheral part of the substrate.
When the substrate is subjected to a surface treatment, such as when the semiconductor wafer is subjected to a gate forming process, the substrate needs to be set on a processing stage with the angular position of its orientation indicator coincided with a predetermined reference angular position.
Generally, a plurality of substrates are held in a vertical stack in a cassette with their orientation indicators positioned randomly. A substrate carrying device carries the substrate from the cassette to an aligner. The aligner holds the substrate carried thereto with the orientation indicator of the substrate positioned at the predetermined reference angular position. Then, the substrate carrying device carries the substrate thus positioned by the aligner to a processing stage and places the substrate on the processing stage so that the angular position of the orientation indicator of the substrate coincides with a reference angular position. A prior edge-holding aligner capable of supporting an edge of a substrate and of adjusting the position of the substrate is disclosed in JP-A No. 2002-151577.
The edge holding aligner disclosed in the above-mentioned patent publication carries a substrate to a rotary holder by a robot hand. The aligner detects a notch in the substrate while the substrate is turned one full turn by the rotary holder, adjusts the angular position of the substrate so that the notch coincides with a reference angular position for the positional adjustment of the substrate.
Then, a lifting holder holds the positioned substrate and lifts up the substrate from the rotary holder. Then, the robot hand takes the substrate held by the lifting holder out of the aligner.
In the edge-holding aligner disclosed in the above-mentioned patent publication, the rotary holder comes into contact with the edge of the substrate to hold the substrate. If the notch lies in an edge region in contact with the rotary holder, the notch cannot be properly detected.
In such a case, the substrate held by the rotary holder needs to be shifted from the rotary holder to the lifting holder or the robot hand. The rotary holder is turned through an angle after shifting the substrate to the lifting holder or the robot hand, the substrate is reloaded on the rotary holder, and a notch detecting operation needs to be repeated. Such a position adjusting procedure using the prior aligner takes much time.
The edge-holding aligner disclosed in the above-mentioned patent publication needs to transfer the substrate from the rotary holder to the lifting holder after the completion of the positional adjustment of the substrate, and the robot hand receives the substrate from the lifting holder. Thus, a transfer operation for transferring the substrate from the rotary holder to the lifting holder is indispensable. There is a high possibility that the thus correctly positioned substrate is dislocated during the transfer operation. The transfer operation increases time necessary for the positioning operations including a feed operation for feeding the substrate to the aligner and a delivery operation for carrying away the positioned substrate.
Accordingly, it is an object of the present invention to provide an edge-holding aligner capable of holding the substrate at an edge region where an orientation indicator is not formed and of completing the positional adjustment of the substrate in a short time.
Another object of the present invention to provide an edge-holding aligner capable of widening a range in which a substrate can be transferred from the edge-holding aligner to a substrate carrying device without shifting the substrate.